Liver fibrosis is a scarring process that occurs in most of chronic liver diseases. While liver fibrosis can progress to cirrhosis, it is also reversible. Hepatic stellate cells (HSC) play a crucial role in the development and regression of liver fibrosis. During liver injury, quiescent HSC (qHSC) transdifferentiate to myofibroblasts-like activated HSC (aHSC) that produce extracellular matrix proteins and fibrogenic cytokines. During the regression of liver fibrosis, aHSC are removed by apoptosis or inactivated to a quiescent stage. A half of aHSC have been shown to be inactivated during the regression of liver fibrosis. Therefore, regulation of HSC activation/inactivation is a critical target for the prevention/therapy of liver fibrosis. No anti-fibrotic drugs have yet reached the clinic to date. Or limited knowledge of molecular players critically involved in the development or regression of liver fibrosis has been a primary challenge to the development of an effective anti-fibrotic therapy. Our previous studies using various experimental model systems have demonstrated novel findings that histone deacetylase 9 (HDAC9) play a critical role in the regulation of HSC activation; and astaxanthin (ASTX), a xanthophyll carotenoid, inhibits the fibrogenic action of HDAC9. Importantly, the inhibitory effect of ASTX on HDAC9 does not only prevent HSC activation, but reverts aHSC to a quiescent state, suggesting that ASTX may be able to prevent and regress liver fibrosis. To expand our novel observations, identifying gene signatures associated with liver fibrosis that are under the regulation of HDAC9 and ASTX is critical. The OBJECTIVES of this project are to conduct a genome- wide transcriptome analysis to identify new HDAC9-regulated genes by which the anti-fibrogenic effect of ASTX is mediated, and to corroborate the findings in vivo as well as in human liver specimens of various chronic liver diseases. As guided by our strong preliminary observations, we establish CENTRAL HYPOTHESIS that HDAC9 is a pro-fibrotic mediator involved in the activation of qHSC. By repressing HDAC9, ASTX exerts an anti-fibrotic action, preventing HSC activation and facilitating the inactivation of aHSC in the liver. The inhibitory effect of ASTX on HDAC9, in turn will prevent the development of liver fibrosis and regress the fibrotic condition, ultimately preventing the progression of fibrosis to cirrhosis. This hypothesis is supported by our strong preliminary results and we will test the hypothesis by pursuing the following three SPECIFIC AIMS: 1) To perform genome-wide transcriptome analysis to identify fibrogenic molecular mediators regulated by HDAC9 and ASTX in HSC from wild-type (WT) and Hdac9 knockout mice; 2) to determine the effect of HDAC9 and ASTX on the prevention and regression of liver fibrosis in vivo using two fibrosis mouse models, i.e., WT and Hdac9 knockout mice with CCl4-induced or diet-induced liver fibrosis; and 3) to validate candidate fibrotic genes in HSC regulated by HDAC9 and ASTX in vivo and in human fibrotic livers. Large IMPACT on public health is anticipated upon completion of this study as the new gene targets will be identified to establish effective and safe strategies for the prevention and therapy for human chronic liver diseases manifesting fibrosis.